When did requiring a card for free API credits help—or hurt?

If you run an API or AI product with a free allowance, did requiring a card actually reduce your costs without killing activation?

I’m researching whether there’s room for a small tool that checks credit grants, rather than another generic signup filter. The part I can’t establish from product pages is whether repeat accounts cost enough to justify another integration. A hundred fake signups that never consume credits may matter less than three that do.

I’d like to hear about a recent change you made: what was being consumed, what control you tried, and what happened to legitimate users. Rough ranges are fine. If email checks, quotas or an existing service solved it cheaply, which one worked?

I’m comparing this with other small software ideas before building. No product to pitch yet—trying to understand whether this is a problem worth paying to fix. Please leave customer details and secrets out of replies.